All, or nearly all, of the injuries sustained during the Boston Marathon bombing, were fake. There may have been some real injuries; but after many hours of careful examination by many dedicated investigators, a verified serious injury from the "bombs" has yet to be found.
For indisputable proof of an "amputee actor" at the Boston Marathon bombing, see - https://archive.org/details/CrisisActorsPreparingDoubleAmputee
Evidence is also being collected, showing that the so-called pressure cooker "shrapnel bombs", did not cause any shrapnel damage, and did not leave any visible evidence that they contained shrapnel at all.
It also appears that the great majority of "doctors" and "EMTs" within the bombing scenes are fake. There are some real firemen and real EMT's on the periphery of the scene, administering real medical treatments (such as IV drip and oxygen). However, consider that if an actor (or anyone else) says that they are having 'chest pains' from stress of anxiety, these people are required by law to treat it as a heart attack, and administer appropriate treatment with no visible injuries. It seems that's what happened in those cases.